With optical elements, such as ophthalmic lenses, one or more marks are often applied to or introduced into a surface of the optical element. Such marks can be used for purposes of, for example, identifying the manufacturer of the optical element, identifying a particular production run that resulted in formation of the optical element, and/or providing information about the optical element, such as optical characteristics (e.g., optical axes, centering points, etc.), the refractive index of the material from which the optical element was fabricated, and/or coatings residing on the optical element, such as antireflective and/or scratch-resistant coatings. Such marks are typically unobservable when the optical element is in normal use, such as being unobservable by a person wearing a pair of ophthalmic lenses that include such a mark or marks. The marks can be rendered observable under certain limited circumstances, such as by exposure to a particular wavelength of light or applied vapor, so as to determine the information contained in the mark. Typically, the marks are of relatively small dimensions. It is often desirable that the mark be a permanent mark, so the information provided thereby can be accessed more than once and/or at a time after formation of the mark.
A method of introducing a mark into an optical element includes, for example, physically engraving a surface of the optical element, such as with a stylus. Chemical leeching can be used to introduce a mark, such as with optical elements fabricated from silica based glass. Lasers can also be used to introduce a mark into the surface of or within the body of an optical element. Present methods of introducing a mark into an optical element can result in the formation of marks that are undesirably observable, under some conditions, when the optical element is in normal use. For example, progressive ophthalmic lenses typically include one or more marks that can be used by an optician to properly and accurately fit the lenses on a person for whom the lenses have been prepared. Such marks can, in some instances, be visually observable to a wearer of the lenses, appearing, for example, as a small area of optical distortion in one or both of the lenses.
It would be desirable to develop new optical elements that include one or more marks that are substantially unobservable during normal use, and which can be rendered observable, such as briefly observable, under controllable conditions.